The human body normally regulates the cardiac output in response to body needs by changing the heart rate, as during physical exercise, and/or by adapting the stroke volume. Under pathological conditions, however, some of the normal regulatory mechanisms may be damaged. For example, heart tissue damaged due to myocardial infarct typically cannot sustain normal pumping function. Although such damage is local in its direct effect on the heart tissue, it can lead to an overall reduction in stroke volume, and hence of cardiac output. The body may react to such a reduction by increasing the heart rate, thus imposing long term strain on the heart muscles, leading in more severe cases to heart failure. There is thus a need for devices and treatments that can regulate the activity of local areas of the heart, so as to compensate for the deficiencies in the normal regulation mechanisms and aid in recovery from infarct and other damaging conditions,
PCT patent application PCT/IL97/00012, and the corresponding U.S. national phase application Ser. No. 09/101,723, which are assigned to the assignee of the present patent application and are incorporated herein by reference, describe methods for modifying the force of contraction of at least a portion of a heart chamber by applying a non-excitatory electrical signal to the heart at a delay after electrical activation of the portion. The signal may be applied in combination with a pacemaker or defibrillator, which also applies an excitatory signal (i.e., pacing or defibrillation pulses) to the heart muscle.
PCT patent application PCT/IL97/00236 and the corresponding U.S. national phase application Ser. No. 09/254,900, which are assigned to the assignee of the present patent application and are incorporated herein by reference, describe a pacemaker that modifies cardiac output. This pacemaker applies both excitatory (pacing) and non-excitatory electrical signals to the heart. By applying non-excitatory signals of suitable strength, appropriately timed with respect to the heart's electrical activation, the contraction of selected segments of the heart muscle can be increased or decreased.
PCT patent application PCT/IL97/00233 and the corresponding U.S. national phase application Ser. No. 09/254,903, which are assigned to the assignee of the present patent application and are incorporated herein by reference, describe methods of applying signals to cardiac tissue in order to modify the behavior thereof.
PCT patent application PCT/IL97/00235, which is incorporated herein by reference, describes a cardiac output controller which applies non-excitatory pulses to the heart in order to increase the heart's stroke volume. Typically, the pulses are timed with respect to the heart's natural activity, and are delivered, for example, during a specific time period of each heart beat.